Digital watermarking (“watermarking”) is a quickly growing field of endeavor, with several different approaches. The present assignee's work is reflected in the earlier-cited related applications, as well as in U.S. Pat. Nos. 5,841,978, 5,768,426, 5,748,783, 5,748,763, 5,745,604, 5,710,834, 5,636,292, 5,721,788, and laid-open PCT applications WO97/43736 and WO99/10837 (corresponding to pending U.S. application Ser. Nos. 08/746,613 (now U.S. Pat. No. 6,122,403) and 09/138,061). Other work is illustrated by U.S. Pat. Nos. 5,734,752, 5,646,997, 5,659,726, 5,664,018, 5,671,277, 5,687,191, 5,687,236, 5,689,587, 5,568,570, 5,572,247, 5,574,962, 5,579,124, 5,581,500, 5,613,004, 5,629,770, 5,461,426, 5,743,631, 5,488,664, 5,530,759, 5,539,735, 4,943,973, 5,337,361, 5,404,160, 5,404,377, 5,315,098, 5,319,735, 5,337,362, 4,972,471, 5,161,210, 5,243,423, 5,091,966, 5,113,437, 4,939,515, 5,374,976, 4,855,827, 4,876,617, 4,939,515, 4,963,998, 4,969,041, and published foreign applications WO 98/02864, EP 822,550, WO 97/39410, WO 96/36163, GB 2,196,167, EP 777,197, EP 736,860, EP 705,025, EP 766,468, EP 782,322, WO 95/20291, WO 96/26494, WO 96/36935, WO 96/42151, WO 97/22206, WO 97/26733. Some of the foregoing patents relate to visible watermarking techniques. Other visible watermarking techniques (e.g. data glyphs) are described in U.S. Pat. Nos. 5,706,364, 5,689,620, 5,684,885, 5,680,223, 5,668,636, 5,640,647, 5,594,809.
Most of the work in watermarking, however, is not in the patent literature but rather in published research. In addition to the patentees of the foregoing patents, some of the other workers in this field (whose watermark-related writings can by found by an author search in the INSPEC database) include I. Pitas, Eckhard Koch, Jian Zhao, Norishige Morimoto, Laurence Boney, Kineo Matsui, A. Z. Tirkel, Fred Mintzer, B. Macq, Ahmed H. Tewfik, Frederic Jordan, Naohisa Komatsu, and Lawrence O'Gorman.
The artisan is assumed to be familiar with the foregoing prior art.
In the present disclosure it should be understood that references to watermarking encompass not only the assignee's watermarking technology, but can likewise be practiced with any other watermarking technology, such as those indicated above.
The physical manifestation of watermarked information most commonly takes the form of altered signal values, such as slightly changed pixel values, picture luminance, picture colors, DCT coefficients, instantaneous audio amplitudes, etc. However, a watermark can also be manifested in other ways, such as changes in the surface micro-topology of a medium, localized chemical changes (e.g. in photographic emulsions), localized variations in optical density, localized changes in luminescence, etc. Watermarks can also be optically implemented in holograms and conventional paper watermarks.)
In accordance with the present invention, various improvements to digital watermarking are disclosed. For example, an improved watermarking method proceeds on an iterative basis in which the watermark data is encoded in a source signal, the result is then decoded, and the “strengths” of the individual encoded bits are discerned. The watermarking parameters are then adjusted so as to redress any deficiencies determined in the first watermarking operation, and the source signal is re-watermarked—this time with the adjusted parameters. So doing assures reliable detection of all the component bits.
The foregoing and other features and advantages of the present invention will be more readily apparent from the following Detailed Description, which proceeds with reference to the accompanying drawings.